fix(eslint-plugin): [no-unnecessary-boolean-literal-compare] preserve boolean result in fixer for nullable true comparisons by paleite · Pull Request #12365 · typescript-eslint/typescript-eslint

paleite · 2026-05-27T08:36:40Z

PR Checklist

Addresses an existing open issue: fixes [no-unnecessary-boolean-literal-compare] Breaks type when using allowComparingNullableBooleansToTrue #3783
That issue was marked as accepting prs
Steps in Contributing were taken

Overview

This updates no-unnecessary-boolean-literal-compare, so autofixes for nullable boolean (e.g. boolean | null, boolean | null | undefined, boolean | undefined) comparisons to true keep returning boolean correctly. Previously, the autofixer was unsafe in value contexts, but correct in condition contexts.

Value contexts

This code snippet:

const isTrue = (x: boolean | undefined): boolean => x === true; // returns a `boolean`

was previously incorrectly autofixed to:

const isTrue = (x: boolean | undefined): boolean => x; // returns the same as the input (`boolean | undefined`) and causes a TypeScript error

That changed the returned value's type from boolean to boolean | undefined. The autofixer now preserves the boolean result:

const isTrue = (x: boolean | undefined): boolean => x ?? false; // returns a `boolean`

Condition contexts

This code snippet:

if (x === true) {}

was previously correctly autofixed to:

if (x) {}

This remains correct because condition contexts only care about truthiness, not about producing a boolean value.

I've included tests to ensure coverage and backwards compatibility.

typescript-eslint · 2026-05-27T08:36:44Z

Thanks for the PR, @paleite!

typescript-eslint is a 100% community driven project, and we are incredibly grateful that you are contributing to that community.

The core maintainers work on this in their personal time, so please understand that it may not be possible for them to review your work immediately.

Thanks again!

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nx-cloud · 2026-05-27T08:37:47Z

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codecov · 2026-05-27T08:43:09Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.75%. Comparing base (54e2857) to head (cc76e2b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #12365      +/-   ##
==========================================
+ Coverage   87.00%   94.75%   +7.74%     
==========================================
  Files         513      223     -290     
  Lines       16570    11398    -5172     
  Branches     5175     3798    -1377     
==========================================
- Hits        14417    10800    -3617     
+ Misses       1463      254    -1209     
+ Partials      690      344     -346

Flag	Coverage Δ
unittest	`94.75% <100.00%> (+7.74%)`	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rc/rules/no-unnecessary-boolean-literal-compare.ts	`100.00% <100.00%> (+4.44%)`	⬆️
...lint-plugin/src/rules/prefer-nullish-coalescing.ts	`95.87% <ø> (+0.55%)`	⬆️
...ckages/eslint-plugin/src/util/isConditionalTest.ts	`100.00% <100.00%> (ø)`

... and 291 files with indirect coverage changes

🚀 New features to boost your workflow:

❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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github-actions · 2026-05-28T08:15:46Z

Hi @paleite, thanks for the update!

Just a quick heads-up: please try to avoid force-pushing moving forward. Rewriting history makes it harder for us to track incremental changes between reviews.

Since we squash merge anyway, there is no need to keep the commit history "clean" on this branch. Standard pushes are much preferred!

…sons

github-actions · 2026-05-28T10:30:39Z

Hi @paleite, thanks for the update!

Just a quick heads-up: please try to avoid force-pushing moving forward. Rewriting history makes it harder for us to track incremental changes between reviews.

Since we squash merge anyway, there is no need to keep the commit history "clean" on this branch. Standard pushes are much preferred!

kirkwaiblinger

Thanks for the PR @paleite!

I think that this PR does address the issue (and the tests look good to me), but some of the code is a little hard to follow, see comments. (note that it was already hard to follow, but I'd like to see if the added logic can be incorporated a bit better into the existing logic.

Also, would you please give the AI Contribution Policy a read and ensure that this PR (particularly the description) complies? Thanks!

paleite · 2026-06-11T08:51:21Z

Thanks for the PR @paleite!

I think that this PR does address the issue (and the tests look good to me), but some of the code is a little hard to follow, see comments. (note that it was already hard to follow, but I'd like to see if the added logic can be incorporated a bit better into the existing logic.

Also, would you please give the AI Contribution Policy a read and ensure that this PR (particularly the description) complies? Thanks!

Thanks for the review. I appreciate having another set of eyes looking at this. As per your request, I addressed (and resolved) the comments you had and rewrote the PR description, so it is now correctly aligned with the changes I did along the way, and it includes some more explanations. I've re-requested a review from you now.

kirkwaiblinger

Made some tweaks to align with #12413, which ended up getting merged first.

Looks good to me! Thanks!

paleite · 2026-06-24T10:42:24Z

@kirkwaiblinger After the alignment, the coverage didn't pass anymore, so I improved it. Once you get some time, I'd appreciate a signoff, and then I'll merge it.

Thanks in advance!

@kirkwaiblinger

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.61.0 | 8.62.1 | | npm | @typescript-eslint/parser | 8.61.0 | 8.62.1 | ## [v8.62.1](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8621-2026-06-29) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-type-assertion] parenthesize object literal at left edge of expression statement ([#12443](typescript-eslint/typescript-eslint#12443), [#12418](typescript-eslint/typescript-eslint#12418)) - **eslint-plugin:** \[no-unnecessary-boolean-literal-compare] preserve boolean result in fixer for nullable true comparisons ([#12365](typescript-eslint/typescript-eslint#12365)) - **eslint-plugin:** \[prefer-optional-chain] use suggestion instead of autofix for trailing binary operator ([#12328](typescript-eslint/typescript-eslint#12328)) ##### ❤️ Thank You - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) - mdm317 - Patrick Aleite - 송재욱 See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.62.1) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website. ## [v8.62.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8620-2026-06-22) ##### 🚀 Features - remove redundant package.json "files" ([#12444](typescript-eslint/typescript-eslint#12444)) ##### ❤️ Thank You - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.62.0) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website. ## [v8.61.1](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8611-2026-06-15) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-template-expression] respect ECMAScript line terminators ([#12388](typescript-eslint/typescript-eslint#12388)) - **eslint-plugin:** \[no-unnecessary-boolean-literal-compare] fix precedence bug in autofix ([#12413](typescript-eslint/typescript-eslint#12413)) - **eslint-plugin:** \[no-unnecessary-type-assertion] wrap object literal in parens when removing TSTypeAssertion in arrow body ([#12394](typescript-eslint/typescript-eslint#12394), [#12393](typescript-eslint/typescript-eslint#12393)) - **eslint-plugin:** \[no-unnecessary-type-assertion] avoid false positive for template literal expressions ([#12281](typescript-eslint/typescript-eslint#12281)) - **eslint-plugin:** \[consistent-indexed-object-style] do not remove comments when fixing ([#12396](typescript-eslint/typescript-eslint#12396), [#10577](typescript-eslint/typescript-eslint#10577)) ##### ❤️ Thank You - Anas [@anasm266](https://github.com/anasm266) - Deftera [@Deftera186](https://github.com/Deftera186) - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) - lumir - Sarath Francis [@sarathfrancis90](https://github.com/sarathfrancis90) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.61.1) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.

@kirkwaiblinger

| datasource | package | from | to | | ---------- | -------------------------------- | ------ | ------ | | npm | @typescript-eslint/eslint-plugin | 8.61.0 | 8.62.1 | | npm | @typescript-eslint/parser | 8.61.0 | 8.62.1 | ## [v8.62.1](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8621-2026-06-29) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-type-assertion] parenthesize object literal at left edge of expression statement ([#12443](typescript-eslint/typescript-eslint#12443), [#12418](typescript-eslint/typescript-eslint#12418)) - **eslint-plugin:** \[no-unnecessary-boolean-literal-compare] preserve boolean result in fixer for nullable true comparisons ([#12365](typescript-eslint/typescript-eslint#12365)) - **eslint-plugin:** \[prefer-optional-chain] use suggestion instead of autofix for trailing binary operator ([#12328](typescript-eslint/typescript-eslint#12328)) ##### ❤️ Thank You - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) - mdm317 - Patrick Aleite - 송재욱 See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.62.1) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website. ## [v8.62.0](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8620-2026-06-22) ##### 🚀 Features - remove redundant package.json "files" ([#12444](typescript-eslint/typescript-eslint#12444)) ##### ❤️ Thank You - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.62.0) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website. ## [v8.61.1](https://github.com/typescript-eslint/typescript-eslint/blob/HEAD/packages/eslint-plugin/CHANGELOG.md#8611-2026-06-15) ##### 🩹 Fixes - **eslint-plugin:** \[no-unnecessary-template-expression] respect ECMAScript line terminators ([#12388](typescript-eslint/typescript-eslint#12388)) - **eslint-plugin:** \[no-unnecessary-boolean-literal-compare] fix precedence bug in autofix ([#12413](typescript-eslint/typescript-eslint#12413)) - **eslint-plugin:** \[no-unnecessary-type-assertion] wrap object literal in parens when removing TSTypeAssertion in arrow body ([#12394](typescript-eslint/typescript-eslint#12394), [#12393](typescript-eslint/typescript-eslint#12393)) - **eslint-plugin:** \[no-unnecessary-type-assertion] avoid false positive for template literal expressions ([#12281](typescript-eslint/typescript-eslint#12281)) - **eslint-plugin:** \[consistent-indexed-object-style] do not remove comments when fixing ([#12396](typescript-eslint/typescript-eslint#12396), [#10577](typescript-eslint/typescript-eslint#10577)) ##### ❤️ Thank You - Anas [@anasm266](https://github.com/anasm266) - Deftera [@Deftera186](https://github.com/Deftera186) - Kirk Waiblinger [@kirkwaiblinger](https://github.com/kirkwaiblinger) - lumir - Sarath Francis [@sarathfrancis90](https://github.com/sarathfrancis90) See [GitHub Releases](https://github.com/typescript-eslint/typescript-eslint/releases/tag/v8.61.1) for more information. You can read about our [versioning strategy](https://typescript-eslint.io/users/versioning) and [releases](https://typescript-eslint.io/users/releases) on our website.

kirkwaiblinger reviewed May 28, 2026

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Comment thread packages/eslint-plugin/src/rules/no-unnecessary-boolean-literal-compare.ts Outdated

paleite force-pushed the feature/preserve-nullable-boolean-compare-fix branch from 7e1459c to 3edd5a2 Compare May 28, 2026 08:15

paleite marked this pull request as ready for review May 28, 2026 08:19

paleite requested a review from kirkwaiblinger May 28, 2026 08:19

paleite added 5 commits May 28, 2026 12:30

fix(eslint-plugin): preserve boolean result for nullable true compari…

48acdf3

…sons

test(eslint-plugin): cover boolean compare fixer branches

185e05c

test(eslint-plugin): format boolean compare branch cases

096d380

test(eslint-plugin): clean up boolean compare cases

4790cf2

Extract conditional test helper

5f94fdb

paleite force-pushed the feature/preserve-nullable-boolean-compare-fix branch from 3edd5a2 to 5f94fdb Compare May 28, 2026 10:30

paleite added 3 commits May 31, 2026 10:48

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

d9c7ba0

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

27c5e74

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

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kirkwaiblinger requested changes Jun 8, 2026

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Comment thread packages/eslint-plugin/src/rules/no-unnecessary-boolean-literal-compare.ts Outdated

Comment thread packages/eslint-plugin/src/rules/no-unnecessary-boolean-literal-compare.ts Outdated

Comment thread packages/eslint-plugin/src/rules/no-unnecessary-boolean-literal-compare.ts Outdated

paleite added 2 commits June 10, 2026 17:47

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

ef0e4ae

fix(eslint-plugin): reuse wrapping fixer for boolean compare

57c517d

paleite requested a review from kirkwaiblinger June 11, 2026 08:51

kirkwaiblinger changed the title ~~fix(eslint-plugin): preserve boolean result for nullable true comparisons~~ fix(eslint-plugin): [no-unnecessary-boolean-literal-compare] preserve boolean result for nullable true comparisons Jun 16, 2026

Merge branch 'main' into review/12365

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kirkwaiblinger previously approved these changes Jun 16, 2026

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kirkwaiblinger added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Jun 16, 2026

kirkwaiblinger changed the title ~~fix(eslint-plugin): [no-unnecessary-boolean-literal-compare] preserve boolean result for nullable true comparisons~~ fix(eslint-plugin): [no-unnecessary-boolean-literal-compare] preserve boolean result in fixer for nullable true comparisons Jun 16, 2026

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kirkwaiblinger dismissed their stale review via bfbada4 June 16, 2026 01:08

kirkwaiblinger previously approved these changes Jun 16, 2026

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paleite added 2 commits June 16, 2026 07:01

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

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Fix coverage

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paleite dismissed kirkwaiblinger’s stale review via 637ff96 June 16, 2026 09:14

paleite requested a review from kirkwaiblinger June 16, 2026 09:29

github-actions Bot removed the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Jun 16, 2026

kirkwaiblinger approved these changes Jun 24, 2026

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kirkwaiblinger added the 1 approval >=1 team member has approved this PR; we're now leaving it open for more reviews before we merge label Jun 24, 2026

Merge branch 'main' into feature/preserve-nullable-boolean-compare-fix

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JoshuaKGoldberg merged commit 301f350 into typescript-eslint:main Jun 28, 2026
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paleite deleted the feature/preserve-nullable-boolean-compare-fix branch June 28, 2026 10:48

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PR Checklist

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Condition contexts

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